It is a general trend that solid state lighting (SSL) devices, such as Light Emitting Diodes (LEDs) or Organic LEDs (OLEDs), move towards SSL devices which are operated at higher voltage and less current, in order to improve the overall efficiency of the SSL devices. SSL devices at high voltage may be constructed by arranging a large number of SSL devices (e.g. a large number of LEDs) in series (using e.g. a monolithic approach or a COB (Chip-on-Board) approach).
SSL devices which are operated at high voltage levels (e.g. in the range of 50V or 150V . . . 200V) may be driven using little to no driver electronics, which leads to low cost. In particular, at low power levels (in the range of 4 W or less), a simple resistor may be used as a current limiter in combination with a high voltage SSL device. Lamp assemblies based on such simple driver electronics suffer, however, from a number of drawbacks, such as a low efficiency (<30 lm/W on lamp level), a high sensitivity to mains voltage changes, and a high sensitivity to the tolerancing tolerances of the SSL device. Furthermore, such lamp assemblies tend to flicker, and are typically not dimmable.
It is a challenge for engineers designing SSL devices overcoming the above mentioned shortcomings.
The present document addresses the above mentioned shortcomings of LED driver circuits.